1. Technical Field
The field of the invention is mobile communications and, more particularly, to enhancing the control of radio interference existing between one or more mobile devices and one or more nearby base stations.
2. Discussion of Related Art
The invention relates to the 3GPP (Third Generation Partnership Project) specification of the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) and more specifically to the Wideband Code Division Multiple Access (WCDMA) High Speed Uplink Packet Access (HSUPA) which is an enhanced uplink feature used in the Frequency Division Duplex (FDD) mode. This feature is being specified in the 3GPP and targeted to 3GPP release 6. A similar enhancement is being done in a high speed downlink packet access (HSDPA).
Referring to FIG. 1, the Universal Mobile Telecommunications System (UMTS) packet network architecture includes the major architectural elements of user equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), and core network (CN). The UE is interfaced to the UTRAN over a radio (Uu) interface, while the UTRAN interfaces to the core network over a (wired) Iu interface.
FIG. 2 shows some further details of the architecture, particularly the UTRAN. The UTRAN includes multiple Radio Network Subsystems (RNSs), each of which contains at least one Radio Network Controller (RNC). Each RNC may be connected to multiple Node Bs which are 3GPP counterparts to GSM base stations. Each Node B may be in radio contact with multiple UEs via the radio interface (Uu) shown in FIG. 1. A given UE may be in radio contact with multiple Node Bs even if one or more of the Node Bs are connected to different RNCs. For instance a UE1 in FIG. 2 may be in radio contact with Node B 2 of RNS 1 and Node B 3 of RNS 2 where Node B 2 and Node B 3 are neighboring Node Bs. The RNCs of different RNSs may be connected by an Iur interface which allows mobile UEs to stay in contact with both RNCs while traversing from a cell belonging to a Node B of one RNC to a cell belonging to a Node B of another RNC. One of the RNCs will act as the “serving” or “controlling” RNC (SRNC or CRNC) while the other will act as a “drift” RNC (DRNC). A chain of such RNCs can be established to extend from a given SRNC ending with a DRNC. The multiple Node Bs will typically be neighboring Node Bs in the sense that each will be in control of neighboring cells. The mobile UEs are able to traverse the neighboring cells without having to re-establish a connection with a new Node B because either the Node Bs are connected to a same RNC or, if they are connected to different RNCs, the RNCs are connected to each other.
One part of the HSUPA feature is a fast Node B controlled scheduling, which enables much more aggressive scheduling due to the possibility to quickly react to overload situations. HSUPA and the fast Node B controlled scheduling are also supported in soft handover. A similar feature may be deployed for the HSDPA and it should be realized that although the description below is mostly confined to the HSUPA, the same principles can be applied to the HSDPA.
The HSUPA scheduling is de-centralized, i.e. each Node B schedules without knowing what the other Node Bs are doing. Still, decisions done in one cell affect to the neighboring cells because of the phenomenon called “other cell interference.” Furthermore, in soft handover, only one Node B may be delivering scheduling commands leading to increased transmission data rate (seen as higher transmission power) to the UE that is actually in connection to multiple Node Bs.
Thus it is quite likely that one scheduling decision may result with an overload or near-overload situation in multiple cells simultaneously. This as such is not a problem as the schedulers in each Node B will independently reduce the data rates of the UEs they can control and thus recover from this situation.
It should however be kept in mind that there is a certain latency from the Node B making a scheduling decision and transmitting the scheduling command before the effect is seen in the uplink interference levels. Because of this the following fluctuation effect may be experienced:                1. The overload situation is detected simultaneously in multiple neighboring cells due to a single interfering UE or multiple interfering UEs that contribute to the uplink interference of multiple cells.        2. Two or more schedulers in neighboring Node Bs will act on the high uplink interference situation by commanding the UEs to lower their data rate (in effect to reduce their transmission powers).        3. The overload condition is cleared for all the schedulers, and they start independently to fill in the freed capacity by admitting higher data rates (i.e. higher transmission powers) for the users they are scheduling.        
This may lead to oscillating uplink interference as there is some delay from the scheduling decision before the actual interference situation is changed and thus multiple schedulers will easily grant higher data rates almost simultaneously and then again reduce the data rates rapidly due to overload situation that occurred due to multiple UEs increasing their transmission powers.